/*
In dot empty argument using "" is to change to default value
*/
digraph "emptyarg"
{
 node [color="red"]
 /* color is default red */
 a;
 /* color is now default black */
 b[color=""];
 a->b;
 /* switch to default */
 node [color=""];
 /* color is defauklt black */
 aa;
 /* color is green */
 bb [color="green"];
 aa->bb;
}
